1. Field of the Invention
The present invention relates to an image forming apparatus which uses an electrophotographic system or an electrostatic recording system.
2. Description of the Related Art
Conventionally, an image forming apparatus based on an inline color system having a configuration wherein a plurality of image bearing members are arranged in the direction of rotation of an intermediate transfer member is known as an image forming apparatus, such as a laser beam printer. This image forming apparatus uniformly charges a photosensitive drum serving as an image bearing member by charging means, develops a toner image by developing means from an electrostatic latent image formed on the photosensitive drum by an exposure device, and transfers the toner image primarily to the intermediate transfer member. Thereupon, a full-color toner image is formed on the intermediate transfer member by repeating the same primary transfer step for each of a plurality of colors. Subsequently, the full-color toner image is secondarily transferred to a recording material, and the full-color toner image is fixed to the recording material by fixing means. Here, so-called single-component contact development is employed as the developing means. When forming an image, the electrostatic latent image on the photosensitive drum is developed by placing a developing roller which serves as a developer bearing member in contact with the photosensitive drum. Furthermore, when not forming an image, the developing roller is separated from the photosensitive drum.
The toner remaining on the intermediate transfer member (untransferred toner) which has not been transferred to the transfer material in the secondary transfer step must be removed from the intermediate transfer member. Japanese Patent Application Publication No. H9-50167 proposes a so-called simultaneous transfer and recovery system as a method for removing the untransferred toner from the intermediate transfer member. More specifically, the untransferred toner on the intermediate transfer member is reverse-transferred to the photosensitive drum in the next primary transfer step, due to the toner being charged with the opposite polarity to the normal charged state of the toner, by toner charging means. The toner which has been reverse-transferred to the photosensitive drum is eliminated by cleaning means, such as a cleaning blade. Moreover, Japanese Patent Application Publication No. 2009-205012 proposes a method using a conductive brush member and a conductive roller member as a method for recovering untransferred toner on the intermediate transfer member (called “secondary untransferred toner” below). More specifically, the secondary untransferred toner on the intermediate transfer member is mechanically scattered, primarily recovered and charged by applying a DC voltage to the brush member.
By adopting a configuration such as that in Japanese Patent Application Publication No. 2009-205012, recovery can be performed simultaneously with the primary transfer step for printing the next page, and it is possible to form images continuously without slowing the print speed. Furthermore, the secondary untransferred toner on the last page of a series of continuous prints is recovered by the cleaning blade of the photosensitive drum, when image formation is not being carried out. Subsequently, by alternately applying positive and negative voltages to the brush member, the primary recovered toner collected on the brush member is expelled onto the intermediate transfer member. Furthermore, when there is a large amount of the primary recovered toner in the brush member, for example, when there is a large number of continuous prints in a series, then printing is interrupted temporarily (image non-formation state) in order to maintain the toner charging performance of the brush member. The toner collected on the brush member is then expelled. Since the recovery of the secondary untransferred toner on the last page and/or the recovery of the expelled toner from the brush member is carried out when image formation is not being performed, then these steps are carried out with the photosensitive drum and the developing roller in a separated state.